Wind farms usually comprise a plurality of wind energy installations, wherein the power generated in the wind energy installations is first fed into a grid internal to the wind farm. At a transfer point, the power is fed out of the grid internal to the wind farm into an external supply grid. Usually the grid internal to the wind farm is a medium-voltage grid, whereas the external supply grid is a high-voltage grid. A transformer with which the voltage of the medium-voltage grid is transformed to the voltage of the high-voltage grid is then provided at the transfer point.
As a result of the high electrical power installed in a wind farm, the connection of such wind farms to supply grids is not without problems. In particular it is necessary to pay attention to maintaining a high electrical quality in the supply grid. Amongst the ways in which this is ensured is that the wind farm that is connected to a supply grid has to observe strict specifications governing the quality of the supplied power. Thus, for example, the power fed into the supply grid must maintain a certain ratio—known as the power factor—between the reactive power and the real power. Even when disturbances occur in the supply grid, the requirements for the quality of the supplied power must be maintained. One example of such disturbances are voltage dips that can result from a short circuit or from a sudden failure of generating station output power.
A farm regulatory device, also known as the “farm master”, is usually provided in wind farms; it functions as a high-level control apparatus for the individual wind energy installations of the wind farm, and can send control signals to the control equipment of the individual wind energy installations. The farm regulatory device thus has the task of monitoring and ensuring maintenance of the requirements for feeding electrical power into the supply grid. The farm regulatory device is therefore designed to affect the control apparatus of the individual wind energy installations in such a way that the requirements for feeding electrical power to the supply grid are indeed satisfied at the transfer point. The farm regulatory device here in particular has the task of monitoring and regulating the reactive power delivered to the supply grid, for which purpose it determines setpoint values of reactive power for the individual wind energy installations and is able to convey them to their control units. The regulation of the reactive power by the farm regulatory device can be oriented around the complex power measured at the transfer point, or the voltage in the supply grid.
If a disturbance occurs in the supply grid, the farm regulatory device of a wind farm calculates new setpoint values of reactive power for the individual wind energy installations of the wind farm in accordance with the prior art. These setpoint values of reactive power are then passed to the individual wind energy installations and have an effect on their control. The calculation and communication of the setpoint values of reactive power does take a certain amount of time, which means that, at least in the case of a disturbance in the supply grid, the requirements on the quality of the power supplied by the wind farm cannot be satisfied continuously.